One of the many ways you can tell that humanity has evolved incorrectly is that there’s no real custom for how to react when someone coughs.  Mostly people just ignore it. If someone’s really hacking up a lung, you might hear “Are you okay?” or “Do you want a glass of water?” But generally, there is no accepted phrase or expression.

This is in direct opposition to the sneeze, which immediately generates any one of several predetermined social responses--despite not being all that different from a cough in terms of noise or its overall disturbance factor.

That’s why you may hear very different responses to each:

SNEEZE: “Bless you!”

COUGH: “Get the hell away from me, germfarm. If you get me sick before I can attend my kid’s violin recital tonight, I’m sending a virus along with your next budget spreadsheet.”